Cooling apparatus



Jan. 5, 1937'- c. F. RITCHIE ET AL COOLING APPARATUS Original Filed July16, 1929 Patented Jan. 5, 1937 UNITED STATES COOLING APPARATUS Originalapplication July 16, 1929, Serial No.

378,745. Divided and this application Novemher '7, 1932, Serial No.

4 Claims.

This invention relates to an apparatus utilized in the separation ofpotassium chlo-rid, (potash), from liquors containing the same, togetherwith borax. In particular, this invention relates to an apparatus usedin the precipitation of potassium chloride from liquors which likewisecontain sufiicient borax to cause, under normal conditions of operation,a precipitation of both potassium chloride and borax.

This application is a division of our copending application, Ser. No.378,745, filed July 16, 1929, now Patent 1,921,481.

One object or" the present invention is to provide an efficient andeconomical system for rapidly cooling a hot concentrated solution ofpotassium chlorid and borax, thereby bringing about precipitation ofpotassium chlorid and simultaneously producing a state ofsupersaturation With respect to borax.

Another object of the invention is to provide a system in which thedesired results may be achieved to the best advantage, at the same timeproducing crystals or potassium chlorid of superior quality with respectto size.

Other objects and advantages of the invention will appear as thedescription proceeds.

While the present invention is described in terms of potassium chlorideand borax, it is obvious that the system of procedure and equipmenthereinafter described may be of value for the manipulation of anysimilar liquor having like characteristics.

Time is the essence of the basic principle, as set forth in the priorart of United States Letters Patent No. 1,343,401, involved in theprecipitation of potassium chlorid and the simultaneous supersaturationof the liquor with respect to borax. By cooling hot concentrated liquorvery rapidly, potassium chloride may be caused to separate withoutsubstantial precipitation of borax. The faster the cooling and theshorter the time of subsequent retention of the supersaturated liquor,the greater will be the satisfaction derived from the process.

The desirability of evaporative cooling procedure has been known forsome time. Its advantages, as applied to the rapid cooling of potassiumchloride liquor, are set forth herein, together with such improvementsto equipment, of the prior art, as specified in United States LettersPatent No. 1,676,277, as render the equipment most efiicient forproducing results superior to those heretofore obtainable.

Hot concentrated liquor containing potassium chloride and borax may beproduced by the high Per cent KCl 18 .8 NazBiOv 5.9

Na2CO3 7.8

NacSO4 1.7 NaCl '7 .1 Unreported 2 .6

Water 54.9

Total 100.0

For the most efiicient operation of a process recovering potassiumchloride and borax from Searles Lake and similar brines, it is thepractice to produce a hot concentrated liquor essentially saturated withthe potassium. compound. Other components appear in the hot concentratedliquor in such quantities as may result from the phase rule solubilityrelationships or as may be determined by the relative quantities in theoriginal brine. A small quantity of water is usually added to theconcentrated liquor to compensate the water evaporated, therebypreventing the precipitation of undesirable salts upon evaporativecooling.

Liquor of the above composition may be cooled to relatively lowtemperatures Without precipitation of components other than potassiumchloride salts and boraX. By the process of the prior art of UnitedStates Letters Patent No. 1,343,401, such hot concentrated liquor israpidly cooled, thereby bringing about precipitation of potassiumchloride .and incurring supersaturation with respect to borax. After theremoval of a precipitated potassium, by means of a filter or acentrifugal machine the boraX is caused to precipitate by seeding,further coolingor prolonged. retention, and thereafter removed from theliquor. The remaining mother liquor, containing valuable potassiumchloride and borax concentrations, is returned to the evaporation orleach system.

. We have carried out the rapid cooling of hot concentrated potassiumchloride liquor in the conventional type of heat transfer equipment, forexample, in tanks containing pipes through which a cooling liquid iscaused to circulate, otherwise known as indirect coolers. While suchequipment produces acceptable results, it has been found thatevaporative cooling equipment is far superior, both with respect toeconomy of equipment and operation and also with respect to the resultsproduced. While the advantages of an evaporative cooler are manifold ascompared with indirect coolers, its greatest advantages, in the presentinstance, reside in the following: provision of a hermetically sealedsystem, freedom from excessive crystal deposits and large handlingcapacity, resulting in relatively short time of liquor retention.

We have found that one of the contributing causes to the destruction ofthe supersaturation of liquor with respect to borax is the infiltrationof borax laden air into the cooling tanks. In .a plant manufacturingborax, it is impossible to prevent a certain amount of fine borax frombeing dispersed into the air. When fine borax crystals are brought intocontact with liquor supersaturated with respect to borax, the liquor issaid to become inoculated, and crystallization ensues. In the old stylecooling tanks, which were usually open to the air and operated in adiscontinuous or batch manner, the supersaturated liquor often becameseeded, and borax crystallization resulted. The use of continuousevaporative cooling equipment to a large extent, prevents trouble fromthis source. In continuous, reduced-pressure, evaporative coolingequipment outside air, usually laden with borax particles, is rigidlyexcluded. Hence; the maintenance of borax supersaturation in the liquor,so vital to the successful operation of the process, is more easily andcompletely realized in evaporative cooling equipment, than in theindirect cooling equipment of the prior art.

Excessive crystal deposits which form upon heat transfer units of theconventional type of indirect coolers constitute a liability to smooth,continuous operation. Wash water must be supplied for the removal ofsuch deposits, thereby causing a loss of the valuable crystals, as wellas holding up operations, involving extra labor expense, et cetera. Theuse of properly designed evaporative cooling equipment, such as thatspecified in United States Letters Patent No. 1,676,277, almost entirelyeliminates the formation of crystal deposits. Furthermore, due to themechanism of the heat transfer involved in the latter case, excessivelocal cooling is prevented.

The present inventors have successfully operated such equipment for longperiods without appreciable crystal deposition. Furthermore, we havefound that more complete and dependable supersaturation of the liquorwith respect to borax may be maintained than with indirect coolers. Theuse of evaporative coolers has proven eminently more satisfactory forconducting the process of United States Letters Patent No. 1,343,401,than coolers known to the prior art.

Time is the essence of the above process. Due to the inherent featuresof indirect coolers it is difficult to cool large volumes of liquor inmuch short of 1-2 hours. Although desired results were obtainable bythis method, it often happened that, for one cause or another, thesupersaturation of the liquor was destroyed and borax crystallizationtook place. Such occurrences, of course, required the rejection of acertain amount of potassium chloride, as well as a complete washout ofthe system with hot water. The capacity of evaporative cooling equipmentis materially greater than indirect cooling equipment, due in part tothe better heat transfer mechanism involved and likewise to the factthat the efficiency of heat transfer remains constant regardless of thelength of time the equipment has been in operation. In the old styleindirect coolers, fitted with an excessively large cooling area, from 1to 2 hours was required to cool a 3000 gallon batch of liquor. We haveoperated a normally designed evaporative cooler, holding 3000 gallons ofliquor, over extended periods at the rate of 100 gallons per minute,with results far superior to those obtained in the former case. Theaverage time of retention of liquor within such a cooler istheoretically 30 minutes. For carrying out the process of United StatesLetters Patent No. 1,343,401, evaporative coolers are in many wayssuperior to indirect coolers.

By the apparatus of the present invention, hot concentrated potassiumchloride liquor is cooled from its high temperature of production to thedesired low temperature entirely by evaporative cooling. Furthermore,said cooling is accomplished in two steps, both embracing evaporativecooling. This scheme possesses a combination of practical advantagesover prior efforts where the operation has been attempted in a singestep, or by other means different from the present invention.

Hot concentrated liquor produced, from Searles Lake or similar brines,for the recovery of high grade potassium chloride is essentiallysaturated with KCl at a high temperature, 200-240 F. However, suchliquor seldom contains sufiicient borax to produce saturation at thattemperature. The liquor of the above analysis was found to be saturatedwith respect to borax at approximately 130 F. this temperature will, ofcourse, differ with variations of the processes employed, but it isadvantageous to maintain it as low as possible. We take advantage ofthis fact in the operation of the improved process of this invention. Bycooling only to the saturation point with respect to borax in the firststep of evaporative cooling no liability of crystallization is incurred.The system is hermetically sealed; so no borax seed is allowed to enterthe system, causing precipitation of borax in the subsequent coolingstep. In this cooling from ZOO-230 F. to approximately 130 F. thegreater portion of the sensible heat of the liquor is removed and thegreater portion of the potassium chloride available is precipitated.Since borax crystallization is impossible at this temperature, equipmentsuch as that specified in United States Letters Patent No. 1,676,277 maybe successfully employed.

The advantages of such equipment for cooling, in general, have been setforth hereinabove. The advantages of the circulation of sludge, asprovided by that equipment are set forth below in connection withcertain improvements we have made to that end.

We have found that, aside from the various factors, hereinabovementioned, contributing to the destruction of the supersaturation ofborax, there exists another factor which is likewise very active. Thisis the force known to those of the crystallization art as mechanicalstimulus. The phenomena of mechanical stimulus is utilized by nearlyevery chemist who, desiring to bring about precipitation of asupersaturated component, scratches the sides of a beaker with astirring rod or similar object. We have found that mechanimercialequipment in several ways.

'cal stimulus may be brought into play in com- Centrifugal pumps (andothers) are very detrimental to the stability of a supercooled boraxsolution. Also, we have found that forcing liquor, especially onecontaining solids (potassium chloride) through excessive lengths of pipelines is effective in destroying the supersaturation characteristics ofthe component in question (borax). We do not believe this effect due toan unreasonably long time of retention; for the effect is even morepronounced as the rate of flow of the sludge of potassium chloride andliquor supersaturated with borax is increased within the pipes. It isone of the purposes of the process of this invention to provide meansfor rapidly cooling potassium chloride liquor, simultaneouslysupersaturated with respect to borax, in which mechanical stimulus isreduced to a minimum.

In the preferred form of our invention, we employ a condensing mediumconsisting of a saturated brine, of the lowest temperature economicallyobtainable, for producing the desired reduction in temperature in thefinal evaporative cooler. The use of this improved condensing medium hasenabled us tocarry the temperature of the liquor 12 F., or more, lowerthan would have been possible with condenser water of economical origin.By this method we are able to conduct the cooling of concentratedpotassium chloride liquor containing borax to the desired. temperaturewithout the use of expensive artificial refrigeration, as has beenrequired under certain conditions of past practice.

Furthermore, by combination of the aforementioned improved condensingmedium, together with the improved equipment of this invention, we areable to produce a most satisfactory degree of supersaturation of boraxwithin the liquor. In the equipment of our invention the final coolingis carried out in such a manner that forces producing mechanicalstimulus are reduced to a minimum.

The present invention, together with various objects thereof, will bestbe understood from a description of one form or example of an apparatusembodying the invention. There is, therefore, hereafter described withreference to the accompanying drawing the preferred form or example ofan apparatus embodying this invention.

In the drawing, Figure 1 shows an elevation of a suitable secondaryevaporative cooler, having a section cut away to show certain interiorconstruction, and Figure 2 represents a plan of the same taken throughline 2-2. Figure 3 shows an elevation of the settler and certainassociated parts, portions being broken away. Figure 4 shows adiagrammatic elevation of the combination of equipment for carrying outthe process.

Referring to the drawing, we provide a relatively small chamber I,having considerable dome space above the point of liquor inlet 2, toprevent undue splashing and entrainment of the liquor with the ascendingvapors. A baffle plate 3 is provided tospread the incoming liquor andprevent short circuiting. The cooler is so designed and arranged withrespect to other existing equipment that only a very small volume ofliquor is maintained within the equipment. All methods of circulationare rigorously avoided in the construction of this secondary evaporativecooler. Liquor enters the cooler continuously through port 2, isimmediately cooled and passes out through outlet valve 4. Level of theliquor is maintained as shown by the dotted line 2-2,

' tion point.

proximatin'g the "ator near the level of the inlet port 2 As a specificexample of one piece of equipment and a procedure which we have employedfor this final or secondary cooling, the following is given. Liquor atthe temperature of 130 F. was delivered to the secondary cooler, Figure1, at the rate of approximately 150 g.p.m. The bottom of the coolercomprised a 52 circular cone, as shown by 5 of Figure 1. The level ofthe liquor was held to such a height that the cone containedapproximately 600 gallons during normal operating conditions. Liquor wascooled by evaporative means to 90 F. The time of retention was,therefore, approximately 4 minutes. Circulation and other effectsproducing mechanical stimulus were reducd to a minimum. The difficultiesencountered with processes and equipment prior to the inception of thisinvention are entirely overcome by this scheme, a most desirable anddependable supersaturation with respect to borax being maintained at alltimes.

While in the past the element of time and various physical elements havebeen believed to be the controlling factors in the production of asatisfactory degree of supersaturation with respect to borax, we havefound that a certain physical chemical phenomenon is also involved inthe process. Two hydrates of borax are known to exist between thecryohydric point and the boiling point of saturated solutions underordinary pressure conditions. These hydrates are the pentahydrate(NazB4O7.5H2O) and the decahydrate (Na2B4Om10I-I2O). The transitionpoint of the hydrates in pure water is approximately 143 F. In complexliquors such as those resulting from the evaporation and manipulation ofSearles Lake and similar brines, the transition temperature ismaterially lowered. The transition temperature of the pentahydrate todecahydrate in liquor of the preceding composition has been found to beapproximately 86-90 F. At temperatures above the transition point thepentahydrate is stable and will. be precipitated when borax iscrystallized above this temperature. At temperatures below thetransition point the decahydrate is stable and will be crystallized whenborax is crystallized below this temperature.

We have found that the supersaturation of borax is much less stable attemperatures favorable to the formation of decahydrate borax than attemperatures favorable tothe formation of pentahydrate borax, the degreeof supersaturation being constant. In other words, it has been foundmuch easier to produce and maintain a supersaturation of 5 per centNazBrOq at 90-l00 F. than to produce and maintain a supersaturation of 5per cent in the temperature region of YB-85 F.

Since it is the usual practice to recycle liquor back to the evaporatoror leach system after removing a crop of potassium chloride and borax,it may be seen that it makes little difference from an eiiiciencystandpoint whether the liquor be cooled slightly above or slighly belowthe transi- I-Iowever, from the standpoint of maintaining a satisfactorydegree of supersaturation within the liquor being cooled this point isof paramount importance. Hence, for the purpose of precipitatingpotassium chloride from concentrated liquor and simultaneously incurringa satisfactory supersaturation with respect to borax, we have found itadvisable to limit the temperature of cooling to a minimum point, ap-

transition temperature. We have attempted to cool potassium chlorideliquor .to a temperature considerably below the transition point of thetwo hydrates of borax; but have found the resulting supersaturatedliquor to be extremely unstable, decahydrate borax being precipitatedupon the slighest provocation. Hence, in the preferred form of thisinvention it is specified that the liquor be cooled only to a minimumapproximating the transition point of the two hydrates of sodiumtetraborate.

The present invention provides means for economically and rapidlycooling hot concentrated potassium chloride liquor containing borax.wherein a most satisfactory supersaturation of borax is maintained. Thesuccess of the present invention resides largely in the means providedfor avoiding destruction of supersaturation by mechanical stimulus. Theequipment of the present invention provides further means formaintaining the desired supersaturation between the point of itsproduction and the point of separation of potassium chloride from thecold sludge.

When liquor of the preceding composition is cooled as specified herein,to a minimum of 86 F., the resulting sludge of supersaturated liquor andpotassium chloride crystals contains approximately 1.1 pounds ofpotassium chloride crystals per gallon of sludge, or approximately 10%solids by weight. Such a sludge is thinner than can be satisfactorilyhandled in commercial filters or centrifugals. In order to provide athicker sludge for such equipment, it has been found necessary tothicken the attenuated product obtained from the coolers. This step notonly produces a more satisfactory sludge for centrifugal or filter feed,but also removes a large proportion of the supersaturated liquor fromthe sphere of the precipitated potassium chloride, thereby reducing thepossibility of precipitation of borax.

It has been pointed out that liquor supersaturated with respect to boraxhas been found to be very susceptible to mechanical stimulus produced bypumps. In order to avoid this undesirable effect, we so arrange thesecondary cooler of this invention with respect to the settling orthickening equipment, that no mechanical handling will be required.Referring to Figure 1, the cooled liquor is passed continuously from thesecondary evaporative cooler I, down line 6 to a suitable settler l ofFigure 3. We prefer to employ a settler of the simplest possibleconstruction. Since undue liquor retention is not desired, the volume ofthe settler is maintained as small-as possible. A 45 or 60 conicalsection has been found quite satisfactory for this service. Agitators 0rscrapers are avoided unless the nature of the sludge is found to be suchas to require their installation within the settler.

The secondary evaporative cooler I of Figure l is placed above thesettler l of Figure 3, in such a manner that sludge will flow by gravityinto the settler. The elevation of the cooler above the settler is suchthat the column of liquor in the connecting line 6 will be sufficient tobalance the reduced pressure inside the evaporative cooling equipmentwith the existing atmospheric pressure.

Referring to Figure 3, pipe 6 terminates into a distributing cup 8placed beneath the surface of the liquor in the settler I. This cup orsimilar device serves to deflect the downward force of the liquor,preventing undue turbulence in the lower portions of the settling cone.As sludge is passed through cup 8 into the settler 1, liquor flows fromthe center toward the outside edge and into launder 9 from whence it maybe withdrawn through outlet ID. A leveling ring ll may be provided forcausing uniform distribution of the overflowing liquor, or other similardevices may be employed. As liquor passes transversely from the centralcup 8 toward the launder 9, potassium crystals settle into the bottom ofthe cone. the bottom by means of a valve l2, a suitable orifice, abalanced density valve or other similar mechanisms. In this manner, weare able to combine the usual barometric seal with the necessarysettling equipment, thereby obtaining results superior to thoseheretofore obtainable. The elimination of pumps, made possible by thiscombination, has eliminated difliculties previously encountered,resulting from the destruction of the borax supersaturation of the coldliquor by mechanical stimulus.

The equipment of United States Letters Patent No. 1,676,277 has beenfound to be well suited to the primary cooling of hot concentratedpotassium chloride liquor to the point of saturation with borax. Duringsuch cooling a large proportion of the available potassium chloride isprecipitated. In order to increase the efficiency of the subsequentsettling operations, as well as those of filtering or centrifuging anddrying, it is desirable to produce a potassium chloride crystal ofrelatively large size and good structure. It has been found that ifconcentrated potassium chloride liquor be subjected to flash evaporation(cooling) very fine crystals are produced. The thermal circulationspecified in the above-mentioned patent, has been found of value inproducing rela tively larger potassium chloride crystals than thoseobtainable when flash evaporation is tolerated. Large amount of coldliquor is mixed with small amount of hot liquor, thereby preventingundue flashing.

Other advantages of the circulation of liquor have also been set forth.We have found that if a small quantity of hot concentrated liquor bemixed with a large quantity of cooled liquor containing suspendedpotassium chloride crystals and the resulting mixture at a relativelylow temperature be introduced into the evaporative cooler, theebullition takes place in a regular and orderly manner. The presence ofthe large quantity of potassium chloride crystals, provided by suchcirculation, causes the potassium chloride content of the hot liquor tobe deposited, to a large extent, upon the potassium chloride crystalsalready present resulting in the production of the desirable largecrystal potassium chloride.

We have been able to increase the desirable effect of sludge circulationin the primary step of the process of evaporative cooling by supplying apump in the closed circuit comprising the depending legs and theevaporative cooler.

Referring to Figure 4, the prescribed circulation pump is shown as 22placed in the closed circulation system comprising pipes 2|. Heretofore,thermal circulation has been employed. While for the most partsatisfactory, the rate of flow, in many cases, has been found to beinsufficient for bringing out the maximum desired eifects. Also, in thecase of thermal circulation some difficulty has been experienced withshort circuiting; a reversal of flow direction taking place probably dueto slight obstructions in the discharge side of the closed circulationsystem, resulting in hot liquor being passed from the system through theoutlet normally handling cooled liquor. The satisfactory utilization offorced circulation in the primary step of evapora- A thickened sludgemay be withdrawn at tive cooling of hot concentrated potassium chlorideliquor containing borax is made possible by limiting the temperature ofcooling therein to the temperature of saturation with respect to borax.By this method, all possibility of borax precipitation is eliminated andconditions most favorable to the crystallization of potassium chloridemay be realized. Large size equipment may be employed, thereby reducingthe capital outlay required. For example, We have found that a primaryevaporative cooler suitable for cooling 100 gallons per minute of hotconcentrated potassium chloride liquor from 230 F. to 130 F. may be of3000 gallons (net) capacity. The average time of retention of liquorwithin the cooler is theoretically 30 minutes. However, due to thecontinuous mixing and circulation, some liquor is retained even agreater length of time. Such equipment, if operated for cooling to thedesired low temperature in a single step is not satisfactory;crystallization of borax being the inevitable result.

The foregoing sets forth the nature and advantages of the process ofthis invention as applied to the problem of producing satisfactorypotassium chloride crystals from hot concentrated liquor containing thesame together with borax, simultaneously incurring a satisfactorysupersaturation in the liquor with respect to borax. The elevation ofFigure 4 sets forth a combination of equipment in its proper order,suitable for carrying out the improved process of this invention.

In Figure 4, 28 represents a suitable tank for storing the hotconcentrated liquor essentially saturated with potassium chloride andcontaining appreciable quantities of borax. Liquor is withdrawn fromthis storage tank by means of a pump 26. In the preferred form of theinvention, we employ a constant level tank 24 for maintaining acontinuous, constant, automatic feed to the primary evaporative cooler.Such a tank, of a suitable design, is supplied with hot liquor by a pump26, in excess of that required by the cooler. Excess liquor flows backthrough a line 21 to the storage tank 28, or into the suction side ofthe pump 26, as shown. The constant level tank 24 is so placed withrespect to the evaporative cooler 31] that the reduced pressure willmaintain the level of the liquor therein at a predetermined height.

In accordance with the advantages hereinbefore described, a pump 22 isemployed for circulating sludge from the primary evaporative cooler,mixing it with a small proportion of hot liquor and returning it to theevaporative cooler. To this end, hot liquor from the constant level tank24 is led into the suction side of the circulation pump 22.

In the layout herein described the circulation pump 22 is made of 600gallons per minute capacity. One hundred gallons per minute of hotliquor are introduced through line 23, the warm mixture entering theevaporative cooler at some convenient point, as shown at 29.

The inlet port 29 may be caused to enter the chamber 30 tangentiallythereby producing a swirling motion of the contents thereof, causingthorough mixing and preventing excessive splashing and foaming. Level ofthe liquid is usually maintained considerably above the point of inlet29, the evaporative cooler being designed to allow sufficient dome spacefor preventing excessive splashing and entrainment of liquor with thevapors passing out through line [9. By

maintaining the level of the liquid considerably above the inlet 29flashing is avoided even when a rapid circulation of brine is employed.A single primary evaporative cooler of the present invention may containapproximately 3000 gallons of liquor, the cylindrical section being 8feet in diameter.

A separator ii is provided for recovering liquor passing over with thevapors, and is connected by a vapor line 26 with a barometric condenser32. Said barometric condenser may be of standard design. In theparticular process of this invention it is supplied with any suitablewater of such a volume as is required to bring about cooling at thedesired rate. Heated condenser water passes down the barometric leg llinto a hot well is, from whence it may be removed by means of a suitablepump, not shown, and sent to atmospheric cooling towers forreconditioning. A vacuum pump or jet exhauster, not shown, is usuallyprovided in conjunction with the barometric condenser for the removal ofnon-condensable gases.

Liquor is cooled in the chamber of the primary evaporative cooler 30 toa temperature approximating the point of saturation with respect toborax, i. e., under the aforementioned conditions, to approximately 130F. Cooled liquor (sludge) is removed by means of line l5 and pump Hi anddelivered to the second step of the improved evaporative cooling processof this invention via lines 16 and 2. Liquor trapped in the separator 31may also be returned by means of a suitable line to the suction side ofthe transfer pump it, or other suitable disposition may be made thereof.

While sludge may be obtained for delivery to line l6 from thecirculation leg 2|, we prefer to provide a separate line, as shown;removing the sludge from the apex'of the cone forming the bottom of theprimary evaporative cooler 3E].

The product from the primary evaporative cooler 36 is deliveredcontinuously to the secondary evaporative cooler l. Details of theconstruction and operation of the secondary evaporative cooler have beenset forth hereinbefore and are illustrated in Figures 1 and 2. Only asmall volume of liquor and no circulation or undue agitation aremaintained in the secondary evaporative cooler. In the case which hasbeen suc cessfully operated and is being described, 150 gallons perminute of liquor at approximately 130 F. are supplied from primaryevaporative coolers. Liquor level is maintained within the 52 conicalsection approximately at the level of the inlet port 30 about 600gallons of liquor being withheld.

A separator 33 is provided for recovering liquor entrained with thevapors passing oif the cooler through vapor line 34. The separator isconnected with a barometric condenser 35 by means of vapor line 36.

Barometric condenser 35 may be of standard design. In the preferred formof this invention we service the barometric condenser 35 with asaturated brine. By the use of this saturated brine in place of theusual medium (water) we are able to maintain the temperature of theliquor within the secondary evaporative cooler l at least 12 F. lowerthan is possible with water at the same temperature. In this second cooling step of this improved process liquor is cooled to a temperatureapproximating the transition point of the two hydrates of borax, or inthe present liquor to approximately 90 F.

Cold liquor passes continuously from the secondary evaporative cooler Ithrough line 6 into the continuous cone settler I. The advantages anddesign of the settler l have been described hereinbefore and areillustrated by Figure 3. Within the settler I the large crystals ofpotassium chloride produced for the most part by the cooling andmanipulation within the primary evaporative cooler 30, settle rapidly tothe bottom, from whence they may be removed as a thickened sludge forthe final recovery of high grade potassium chloride. Clear liquoroverflows and is utilized in suitable processes embracing the recoveryof boraX, the end liquor being returned to the evaporation or leachsystem for further recovery of the valuable constituents.

Figure 4 and the description thereof represents in a somewhatconventional manner the improved process of the present invention. Itmust be understood that only single units have been shown and manycommon devices used in connection therewith have been eliminated for thepurpose of simplicity. In commercial practice, we may employ a series ofprimary evaporative coolers in parallel, thereby lending flexibility tothe system. The same is true in the case of the secondary evaporativecoolers. In a specific installation, we have employed three primaryevaporative coolers in parallel, feeding g.p.m. of liquor to each,followed by two secondary evaporative coolers in parallel, feedingg.p.m. of the partially cooled liquor to each. Other combinations may bemade without departing from the scope of the present invention.

Observation ports, level gauges, thermometers, regulation valves, vacuumregulators, et cetera, have been omitted from the description, sincesuch equipment is of common knowledge and always employed by competentengineers in the design of such equipment, where required.

We claim:

1. An apparatus for cooling liquor, comprising an evaporator, means formaintaining said evaporator under reduced pressure, means for forciblycirculating liquor from said evaporator and back into said evaporator,means for introducing fresh brine into said circulating means, a secondevaporator, means for passing brine from the first evaporator to thesecond evaporator, and means for maintaining said second evaporatorunder reduced pressure, said second evaporator being of relatively smallcapacity, a sludge thickening means, and means for passing brine fromsaid second evaporator under gravity to said sludge thickening means,whereby liquor flows from the first evaporator through the secondevaporator and to said sludge thickening means without being subjectedto appreciable agitation or mechanical stimulus.

2. In combination in a crystallization apparatus, a primary vacuumevaporative chamber having an inlet, an outlet for cooled liquor, and avapor outlet, means for removing gases and vapors from said chamber toefiect cooling through vaporization of water vapor from the liquortherein, means for circulating the liquor from said chamber and backinto said chamber, a secondary vacuum evaporative cooler of relativelysmaller capacity than said first cooler having an inlet for liquor, anoutlet for cooled liquor, and a vapor outlet, means for applying andmaintaining a vacuum within said secondary cooler, and means fortransferring liquor from said primary chamber to said secondary cooler,whereby liquor flows through said secondary cooler without beingsubjected to mechanical stimulus.

3. An apparatus for cooling liquors comprising a primary evaporator,means for maintaining the evaporator under reduced pressure whereby theliquor therein may be cooled by removal of heat of vaporization, meansfor forcibly circulating the liquor out of and back in said primaryevaporator, means for introducing fresh liquor, a second evaporator,means for passing cooled liquor from said primary evaporator to saidsecond evaporator, means for maintaining said second evaporator underreduced pressure thereby permitting further cooling of the liquortherein by removal of heat of vaporization, and means for dischargingbrine from said second evaporator in such manner that the brine passesbut once through said second evaporator.

4. An apparatus for crystallizing salts from solution by cooling, whichcomprises a vacuum evaporative cooler, means for circulating solutioninto and out of said cooler, means for supplying fresh solution to saidcooler to the external portion of said circulating means, a secondevaporative cooler of relatively smaller capacity than said firstcooler, a crystal separator disposed below said second cooler, and meansfor passing solution and formed crystals from the first cooler once onlythrough said second cooler and to said crystal separator withoutsubjecting such solution to mechanical stimulus during its passagethrough said second cooler to said crystal separator.

CHARLES F. RITCHIE. WILLIAM A. GALE. WILLIAM H. ALLEN.

